As is well known, conventional radios use a crystal oscillator for tuning. It is conventional to store a reference frequency, which is used to assist in accurate tuning of the radio. When the radio is manufactured, the device is tested to determine an appropriate reference frequency to use such that the radio will tune properly given the actual frequency which the oscillator outputs. The actual oscillator signal is input to the radio transceiver, along with the reference frequency, to produce a frequency to accurately tune the radio. In this fashion, data may be received reliably.
However, the frequency which the crystal oscillator outputs may change over time. For example, significant changes may occur to physical characteristics of the oscillator early in the life of the radio device. Consequently, if a user should first turn on the device, for example, several months after it was manufactured, the device may be unable to properly receive data. The crystal oscillator is also sensitive to temperature variations, and hence a radio may have trouble tuning and receiving data if the ambient temperature changes.
Some conventional methods for performing frequency corrections make an estimate of how much frequency correction needs to be applied to compensate for changes to the crystal oscillator. For example, frequency offset samples are taken to estimate the needed frequency correction. However, some methods will only make frequency corrections if the needed correction is large, for example, greater than 400 Hz. This is because of an inherent unreliability of the process of determining the needed correction. Were these methods to make a frequency correction for smaller needed changes, the probability that the radio performance will actually decrease is significant.
Some conventional methods of performing a frequency correction of a radio require that very stringent acceptance criteria be met for each of a number of frequency offset samples (needed frequency corrections). If the criteria are not met for any of the samples, the process starts over. Consequently, while this may help with the accuracy of the frequency correction estimates, it is not efficient. The narrow band of acceptance criteria may comprise requiring that the radio receives: a certain number of channels correctly; a certain number of packets from the channel; and a signal at a minimum strength. Furthermore, the temperature must be in a certain range and the frequency offset (needed correction) must be at least, for example, 400 Hz.
All methods of providing frequency correction should deal with several problems that may cause inaccurate data sampling. For example, noise can interfere with the sampling or the signal itself may be weak. Other causes of invalid frequency sampling data may include other devices operating at the same time, which may cause a false frequency shift. Or, the carrier signal may be floating because the base station has just finished transmitting data. Some conventional methods take several samples over a long period of time to address these problems. Unfortunately, because the sampling and processing take a long time, the ability of the radio to process further data (e.g., accept incoming packets) is hindered.
Consequently, from an end user standpoint, many conventional methods are too time consuming and result in less accurate and too infrequent frequency corrections.